What Happens to Your Brain When You Sleep in a New Environment

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It turns out that there's actually a scientific reason behind why people don't sleep soundly in an unfamiliar place.

According to a recent study published in the journal Current Biology, only half your brain enters deep sleep when you try to go to bed in a strange, new location.

At least during the first night that you sleep in a new environment, the left hemisphere of the brain stays alert while the right hemisphere rests. The biological trait is thought to be a leftover evolutionary advantage that allowed early humans to respond to nighttime threats, NPR reports.

Here's how the study was conducted.

Researchers at Brown University studied the brain wave patterns of 35 students, finding that their slow-wave activity — which occurs when the brain has entered deep sleep — was significantly higher in the right hemisphere during the first night of the study. But after the first night, that difference tapered out, leading researchers to conclude that the brain adjusted after it became familiar with the sleep setting.

"When we're sleeping in a new environment and we don't know how many predators are around, it would make sense to keep half the brain more alert and more responsive to bumps in the night," Niels Rattenborg, who's led studies on avian sleeping patterns at the Max Planck Institute for Ornithology in Germany, told NPR.

To support their conclusion, the researchers played a standard tone on repeat, followed by a single "deviant" tone of a different pitch, while the students slept. In a person who was awake or sleeping lightly, the brain would respond to this aberrant tone. The brains of the sleeping students did the same, but the left hemisphere showed increased activity.

"Then the researchers played a sound loud enough to wake someone who was sleeping lightly," NPR reports. "And they found that students woke up faster when the sound was played into the right ear, which is connected to the left side of the brain."

The evolutionary advantage this brain traits provides is probably less useful to modern humans — making us experience less restful sleep when we spend the night at a hotel or friend's house, for example — but in the animal kingdom, this trait still helps marine mammals such as dolphins, whales, and seals respond to threats, Scientific American reports.